Welded well strainer



Jan. 13, 1970 LAYNE ETAL WELDED WELL STRAINER 5 Sheets-Sheet 1 Original Filed May 14, 1964 Max 5 1 05/06 Theodore W. Maflfim/Jen f/VVf/VTOAJ Jam 13, 1970 LAYNE ET AL 3,489,185

WELDED WELL STRAINER Original Filed May 14, 1964 3 Sheets-Sheet 2 Max lay/7e BY Mwaa Jan. 13, 1970 LAYNE ET AL 3,489,185

WELDED WELL STRAINER Original Filed May 14, 1964 3 Sheets-Sheet 5 Max f. Z ay/y e Thaw are 14/. Manfiauaen f/VI/f/VTO/zd' ATTORNEY;

United States Patent Office 3,489,185 Patented Jan. 13, 1970 3,489,185 WELDED WELL STRAINER Max E. Layne and Theodore W. Munhausen, Houston, Tex., assignors to Layne & Bowler, Inc., Houston, Tex., a corporation of Maryland Original application May 14, 1964, Ser. No. 367,473. Divided and this application Nov. 2, 1966, Ser. No. 591,460

Int. Cl. B21f 3/02, 15/08, 27/10 US. Cl. 140-922 5 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for making welded, wound wire weld screens. A collapsible mandrel made of two longitudinal sections, each defining an are slightly less than 180, provides a temporary support upon which lugged wire is wound and secured by longitudinal welds. The sections of the mandrel are held in the proper cylindrical shape by a plurality of two-part conical wedge arrangements spaced axially along the mandrel. The conical wedges are engaged by corresponding conical surfaces on an axial rod.

This is a divisional application of co-pending patent application Ser. No. 367,473, filed May 14, 1964, by the same inventors.

This invention relates to an improved structure for tubular well strainers and more particularly to well strainers of consistent dimension with the well pipes with which they are used and having flow characteristics provided by a substantially continuous spiral opening.

Commonly a well is completed with a string of casing pipe secured in the well bore and having a screen or strainer at the lower end thereof positioned within the formation from which oil, water, gas production, or the like, is to be obtained. Although the nomenclature is not consistent throughout the industry, in the specification and claims of this patent, the term screen denotes the body of the pipe comprising the openings and the term strainer denotes the screen plus the associated hardware to make up a complete assembly ready for attachment to the casing pipe. The strainer may be a single length of screen pipe (in the industry usually called a joint of screen pipe) perhaps thirty feet long, or it may comprise six or eight or more joints of screen pipe each of thirty foot length.

The producing formation is often quite sandy, resulting in unconsolidated sand particles tending to flow to the screen and clog its openings. Particles of sand and the like that are small enough to pass through the openings in the screen are produced with the production fluid or gas, often cutting elbows, valve seats, etc., along the internal surface of the production string, as well as contaminating the fluid or gas produced.

To greatly reduce undesired contaminates, it is common practice in many producing formations to surround the screen with a pack of gravel to fill the space between the screen and the natural producing formation. By proper selection of gravel particle size much straining action can be built into the gravel pack, thereby reducing screen clogging and the production of sand with the production of oil, water, gas, or the like.

It is also common practice during the drilling and completion of wells and the setting of the gravel pack to use drilling mud of a heavy viscous and colloidal nature. Since this mud also tends to contaminate the production fluid or gas, it is desirable to remove such mud from the gravel pack and its environs before commencement of production. A flushing operation is performed to accomplish this desired cleansing.

A full understanding of certain features in well strainers, and the problems in their manufacture, commands a familiarity with this flushing operation.

A flushing tool, one example of which 53 is illustrated inside a well strainer screen 47 in FIG. 6, is lowered into the well on the lower end of a string of pipe or tubing 54 used as a flushing string assembly until it reaches the bottom of the screen 47.

The flushing tool 54 comprises a length of pipe 56 perhaps two to four feet or so in length and having perforations 63 therein through which flushing fluid may pass outwardly when it is pumped down the string of pipe carrying the flushing tool.

On each side of the perforations, there is fitted a swab cup, 57 and 58, facing each other and adapted slidingly to engage the interior of the well screen, and to expand outwardly in response to pressure between the swab cups from fluid discharge through the perforations so as to sealingly engage the screen interior.

In the common flushing operation, such a flushing tool 53 on the lower end of a string of pipe 54 is located at the lower end of the screen 47 situated in the producing formation 64 in the well bore, and a flushing fluid, commonly water, is pumped down the interior of the pipe 54 and out the perforations 63, being confined by the swab cups 57 and 58 to pass through the screen into the gravel pack 65 and on occasion into the adjacent formation. Circulation of the flushing water is completed through the gravel pack 65 to a level above the upper swab cup 57, then back through the screen 47 into the annulus between the screen 47 and the pipe 54, and upward for conduct to the surface in the annulus between the pipe 54 and the casing, which in this example it is assumed extends to the surface from above the screen 47.

After a period of time sufficient to wash the lowermost location, the flushing tool 53 is raised upward slowly, so that the outward flow of flushing water is moved upward to an area where before the flushing water was moving into the annulus between the screen 47 and the pipe 54 and this area is washed as before. The flushing tool 53 is again moved upward, while flushing water continues to flow, until the entire length of the screen has been washed. The flushing tool 53 may be raised and lowered as many times as desired in continuance of the flushing action until satisfactorily clean water is being returned to the surface.

To obtain satisfactory flushing, a good seal must be achieved between the swab cups and the inside surface of the screen and there must be good fiow characteristics of the water in the return path. Projections from the strainer wall protruding into the center bore will prevent an effective seal. Also, a strainer of different internal diameter from the well pipe will prevent good flow characteristics of the water in the return path, as well as requiring the swab cups to either expand or contract in the strainer from their condition while in the well pipe through which they are lowered and removed.

The majority of prior art structures are typified by Johnson 2,046,459, Harmon 2,323,713, and Westphal 1,546,528. Johnson shows the strainer screen formed by a perforated section of pipe wrapped with wire. The reduced internal diameter of the strainer with respect to the attached well pipe and the double thickness of pipe wherein particles are easily trapped are undesirable characteristics of the Johnson-type structure.

Harmon shows a single thickness of strainer material made from wrapped wire, but the angle irons left on the inside of the structure from internal projections and make effective flushing extremely diflicult because of the poor seat for the swab cups.

Westphals structure is incapable of fabrication with close control of tolerances in other than short lengths. Westphal requires the exceedingly expensive procedure of cutting out the entirety of all of the space forming inlet area permitting the fluid to pass through the resulting screen. The cost of doing that cutting, particularly in the case of stainless steel and other hard metal screens, is absolutely prohibitive and totally forbids the use of the screen of the type disclosed in Westphal. In the well business today most screen is made in 30 to 33 foot lengths to eliminate the problem of having to secure screen sections together as by welding or otherwise, and in such lengths the practical impossibility of cutting the openings as in Westphal to close tolerances is readily apparent.

In accordance with an embodiment of the present invention an expansible mandrel having a smooth external surface is used for establishing a form about which the metal wire is Wound to form the screen. Unlike the prior art structure exemplified in Harmon 2,323,713, the present invention utilizes tapered surfaces as the eX- panding force so as to achieve uniform expansion. Also, the complete absence of projections afiixed to the inside surface of the screen eliminates the possibility of the mandrel sections binding when the mandrel is collapsed.

Because the end product of this invention is dilferent from those in the prior art, methods and apparatuses used heretofore have also been found to be quite dissimilar.

Therefore, described herein is an illustrated embodiment of a well strainer and the method of manufacturing the illustrated embodiment comprising:

Expanding an adjustable collapsible mandrel to an outside diameter equal to the inside diameter, which will be smooth without inwardly protruding ribs or the like, of the screen to be produced;

Deforming metal wire from which the screen is to be formed at spaced intervals and precisely sizing such deformation so as to provide lugs of precise dimension protruding from the sides thereof;

Clamping one end of such wire to the mandrel;

Wrapping the wire helically around the periphery of the mandrel so that each succeeding convolution of the wire is adjacent the preceding convolution except as held apart by the pre-formed lugs of precise dimension;

Clamping the second end of the Wire at a distance, which may be any desired distance without restriction by the practicalities of this manufacturing method, along the mandrel from the first end of the wire, thereby determining the total length of the screen;

Welding beads mostly externally of the internal diameter of the screen to bond together successive convolutions of wire without bonding the wire to the mandrel;

Then collapsing the mandrel to allow the screen to be removed therefrom;

All whereby a screen of any desired length may be economically made with precise control of the screen openings down to fine tolerances and with a smooth interior screen surface facilitating easy and good flushing operations.

More particular description of the invention may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which form a part of this specification. It is to be noted however, that the appended drawings illustrate only a typical embodiment of the invention and therefore is not to be considered limiting of its scope for the invention will admit to other equally effective embodiments.

In the drawings:

FIGURE 1 is a plan view with some parts broken away of a well strainer being constructed in accordance with this invention;

FIGURE 2 is a transverse section taken substantially along the line 2-2 of FIG. 1 of the mandrel radially expanded;

FIGURE 3 is a transverse section of the same view shown in FIG. 2 with the mandrel partly radially collapsed;

FIGURE 4 is an exploded perspective view of the apparatus used'to form the well strainer;

FIGURE 5 is an enlarged view of one end of the well strainer and adjoining connector half in vertical section and half in side elevation; and

FIGURE 6 is a vertical section of the well strainer during flushing operation.

In the drawings, reference numerals have been employed to indicate parts as follows:

. mandrel rod assembly limiting collar limiting collar lower section upper section cylinder end extending end truncated conical surfaces flanges truncated conical surfaces edge edge edge edge rod . conical rod collar conical edge conical edge recess threaded rod end unthreaded rod end inside surface of collar inside surface of collar machine screw washer hole machine screw washer hole washer hole nut . lock nut recess holding pin hole wire clamp flanges holes clamp bolt clamp nut metal wire lugs weldbeads well strainer screen connector groove external connector weld bead internal connector weld bead internal connector threads flushing tool flushing string assembly connector perforate flushing string section swab cup swab cup swab cup holder swab cup holder outer edge of cup outer edge of cup perforations producing formation gravel pack Referring to the drawings, and first to FIGS. 1 and 4, it is seen that the apparatus used for forming the screen of the well strainer comprises principally a mandrel 1, rod assembly 2 and limiting collars 3 and 4. Mandrel 1 comprises two parts, a lower section 5 and upper section 6. Sections 5 and 6 are arbitrarily referred to herein as lower and upper to correspond with their positions in FIG. 4; therefore, this designation is not intended to mean that in use section 5 is always in the lower position and section 6 is always in the upper position.

The lower section 5 forms a complete cylinder at one end 7. Extending from the cylinder end of the lower section is an extending end 8, which is at least as long as the well strainer screen to be formed. A transverse section of end 8 reveals the partial shell of a cylinder describing an arc somewhat less than 180 degrees, on the order of 170 degrees.

Rigidly aflixed internally in this open or cutout extending end 8 is a series of flanges 9 spaced at even distances. Each of these flanges forms one-half of a truncated conical surface with its internal surface 10.

The upper section 6 of mandrel 1 is similar in shape to the extending end 8 of the lower section 5, i.e., a transverse section forms an arc of slightly less than 180 degrees (on the order of approximately 170 degrees), with the section being at least as long as the well strainer screen to be formed. Rigidly affixed to the inside surface of the upper section 6 are a series of flanges 11 similar to flanges 9 in that they have internal truncated conical surfaces 12.

Upper section end 6 complements the extending end 8 so that when the mandrel 1 is in use, edge 13 of the upper section is aligned opposite edge 14 of the lower section and edge 15 of the upper section is aligned opposite edge 16 of the lower section. When sections 5 and 6 of the mandrel are aligned in this position, flanges 9 and 11 internal to the two sections, are diametrically opposed to form approximately continuous surfaces, only separated by the distance which edge 13 is separated from edge 14, as best shown in FIG. 2.

Rod assembly 2, in operation located within the mandrel to expand it and hold it in expanded condition, comprises a rod 17 and a series of conical rod collars 18, there being a rod collar 18 corresponding to each pair of flanges 9 and 11. The external surface of each collar 18 describes a conical slope of essentially the same angle described by the internal surfaces of flanges 9 and 11. It will be seen that preferably only conical edges 19 and 20 come into mating contact with the surfaces of the flanges, there being a recess 21 to minimize friction and sticking between the surfaces. Rod 17 is threaded on the end nearest the smallest diameter of the conical collars at threaded end 22. As will be explained, the operation of the rod assembly 17 does not'require that the opposite end 23 be threaded.

Limiting collars 3 and 4 constitute means for determining the inside diameter of the well strainer screen to be formed by their internal diameters. That is, the surfaces 24 and 25 describe cylinders having the same diameter as the internal diameter of the well strainer to be formed. Collar 3 is held to mandrel 1 via machine screws 26 inserted through washers 27 and tightened into internally threaded holes 28, and in a similar manner, limiting collar 4 is held to the mandrel via machine screws 29 inserted through Washers 30 and tightened into holes 31.

Washer 32, having a central hole 33 that slips over threaded end 22 on rod 17, presses and holds section 6 into correct longitudinal relationship with respect to section 5. Washer 32 is held in position by nut 34 and lock nut 35 screwed onto threaded end 22. The outside diameter of washer 32 is small enough to slip inside of surface 24 of collar 3.

A recess 36 on the inside surface 24 of collar 3 accommodates the lead end of the metal wire to be used for forming the well strainer screen. This lead end is held in place via holding pin 37 screwed into threaded hole 38 in collar 3, which opens into recess 36, thereby constituting means for holding the lead end of the wire. Retaining wire clamp 39 is positioned between collars 3 and 4 and around mandrel 1 at a location along the mandrel that determines the length of the well strainer screen to be formed. That is, the distance between wire clamp 39 and collar 3 determines the length of the screen. After the wire used for forming the screen is completely wrapped, clamp 39 is squeezed together at flanges 40, thereby constituting means for holding the trailing end of the wire. A clamp bolt 42, inserted through holes 41, is secured by clamp nut 43 for this purpose.

In readying the mandrel so that it is in condition for forming screen 47, the lower section 5 of the mandrel is placed so that the open or cutout portion of extending end 8 is facing upward. Rod 17 is inserted by placing non-threaded end 23 into cylindrical end 7 of section 5 and resting conical rod collars 18 on their corresponding flanges 9 located in the mandrel section. The rod is then moved longitudinally slightly in the direction of its non-threaded end.

Upper section 6 is then placed in position over the rod assembly so that edges 13 rest on edges 14 and edge 15 is in contact with edge 16. The flanges 11 in upper section 6 are now exactly positioned over flanges 9 in lower section 5 to form evenly aligned, continuous flange surfaces for contact with the conical collars on rod 17.

Collars 3 and 4 are placed over the mandrel so that they are positioned at the respective opposite ends of upper section 6, which now forms the expansible and collapsible section of the mandrel. For convenience of assembly, collar 3 is positioned preferably to slightly overhang the end of the mandrel by an amount slightly less than the thickness of washer 32. Washer 32 is then placed over rod 17 and into collar 3 so as to abut the end of section 6 and section 5. Nut 34 and lock nut 35 are then screwed loosely onto threaded end 22 of rod 17 to hold washers 32 loosely in position.

Rod 17 is pushed in the direction of its threaded end to radially expand the upper section 6 away from lower section 5, as best shown in FIG. 2. Because the longitudinal movement of rod 17 tends to cause section 5 to slip longitudinal with respect to section 6, it may be necessary to apply a little longitudinal restraining pressure to washer 32 to keep section 6 aligned properly with respect to section 5.

When section 5 is properly expanded to its limit as determined by collars 3 and 4, nut 34 is tightened into fast holding position; lock nut 35 is tightened against nut 34 to secure it in position; and machine screws 26 and 29 in collars 3 and 4 are tightened to hold these collars firmly in position.

The wire selected for forming the well strainer screen is normally stainless steel or other hard metal capable of forming a rigid section. The wire is squeezed or pinched together by stamping small segments at predetermined intervals to form lugs. In the wrapped condition, these Wire lugs provide the necessary spacing between consecutive convolutions to allow proper straining action to occur. Typically, the lugs are stamped to space the Wires apart by an amount almost equal to the diameter of the wires. In the referenced drawings, it will be seen that lugs 45 have been pinched in metal wire 44 at an interval spacing to form twelve lug groups about the periphery of the wire screen.

To form the screen, the entire assembly is placed on a machine capable of rotating it about its center, longitudinal axis, typically an engine lathe, and the lead end of the prepared metal wire 44 is inserted in recess 36 of collar 3 and held in position by holding pin 37 screwed into the threads of hole 38.

The assembly is then rotated to allow the metal wire to be wrapped helically about the circumference of the mandrel. About 40 to pounds of tension is normally used on the wire as it is guided longitudinally along the mandrel in the wrapping operation.

Consecutive convolutions are spaced as close to one another as the spacing lugs will allow, the tension on the wire and the surface of the mandrel being inherent factors that cause the lugs to align themselves parallel to the longitudinal axis of the screen.

When the desired length of Well strainer screen has been prepared, clamp 39 is positioned to receive the trailing end of metal wire 44- and tightened about this end by clamp bolt 42 and clamp nut 43.

An automatic welding machine, any of the types well known in the art, is moved into position opposite one end of the wire helix that has been formed by the metal wire.

The depth of the weld is adjusted to be approximately one-half of the diameter of the metal screen, which is sufficient to create a sturdy bond between the consecutive convolutions of wire but not so deep as to weld the metal wire to the mandrel.

In accordance with ordinary good welding practice, 'such as welding in the presence of an inert gas, the machine is moved along the surface of the screen to form weld beads. In the embodiment of the invention shown in the referenced drawings, six weld beads are illustrated, although it will be understood that any practical number is suitable.

It has been found that continuous bead rows the full length of the well screen are quite satisfactory. However, it is possible to use a series of partial or staggered bead rows forming an even pattern about the Well screen to accomplish comparable results.

To remove the well screen from the mandrel, collars 3 and 4 are removed by loosening machine screws 26 and 29 and holding pin 37. Wire clamp 39 is then released by loosening clamp bolt 42 and sliding wire clamp 39 along the mandrel away from the screen. Lock nut 35 and nut 34 are then unscrewed from threaded end 22 of rod 17. Rod assembly 2 is loosened by pulling longitudinally in the direction of unthreaded end 23.

This allows upper section 6 of the mandrel to collapse toward the lower section 5, as shown in FIG. 3, so that the well strainer is easily removed by slipping it from the end of the mandrel.

Well strainer screen 47 which has been formed is attached to a connector to make an operable assembly, female connector 48 being shown in FIG. 5 for this purpose. Connector 48 is channeled with grooves 49 to guide the connector onto the end of the well screen, there being a corresponding groove 49 for each weld head 46. An external connector weld bead 50 secures the connector to the outside of the screen and an internal connector weld head 51 connects the screen to the inside of the connector. In practice, only external connector weld bead 50 or internal connector weld bead 51 should be sufiicient.

The connector is threaded with threads 52 to facilitate connecting with a well pipe or closed stub.

A male connector, rather than the female connector 48 illustrated, may be used for a specific installation. When used, a male connector is attached by abutting the connector to the end of the well strainer screen and Welding a single external bead, similar to weld bead 50, to bond the screen to the connector.

The well strainer is shown being used in the flushing operation in FIG. 6. Flushing tool 53 is shown lowered into a segment of the Well strainer by means of a flushing string assembly 54 attached to the flushing tool by connector 55. Flushing tool 53 comprises primarily a perforate flushing string section 56 and facing swab cups 57 and 58. Cup holders S9 and 60 attach the swab cups to the body of flushing tool 53.

The outer edges 61 and 62 of swab cups 57 and 58 effectively block oif an area in the channel annulus between the inside of well strainer screen 47 and the outside of perforate flushing string section 56. This means that fluid material flowing in the channel annulus cannot freely flow from the isolated area to the remainder of the annulus without first flowing out through grooved opening 49 to the outside of the screen and back in again after bypassing the swab cups.

To flush with flushing tool 53, fresh water supplied from the flushing string assembly flows out through perforations 63 into the isolated section of the well strainer channel between the swab cups. If the slitted passageways in the screen are clogged, pressure will build up on the channel until it becomes enough to flush out the clogging material.

The return path for the slushing water is above and around cup 57, in through the inlet passageways in the wall of screen 47, and up the channel between the inside of the strainer (and higher up, the inside of the well casing) and the outside of flushing string assembly 54 to the surface of the well.

For a normal well where the contents of the well are pumped only from a single stratum, the well strainer is attached to the well pipe and lowered into the well to the lowest operating depth; the flushing tool is lowered to its fullest extent within the strainer; fresh water is flushed down the flushing tool until clear water is returned up the well pipe; then the flushing tool is raised to the next higher position in the strainer and the process repeated until the entire area of the strainer has been flushed.

If reflushing or partial reflushing is desired, flushing string assembly 54 can be easily lowered to the desired extent and the operation repeated.

It has been mentioned that the length of well strainers in common use today is in the neighborhood of 30 feet. Should a longer well strainer be required for a specific application, sections can be easily joined together via their connectors.

In some well applications, it is desired to draw from two different stratum depths, for instance, from 30 feet and from 60 feet with no desire to draw from the well between these two depths. In this event, one well strainer is lowered to the 60 foot position, a plain well pipe is connected in the area where there is no desire to flush, and a second strainer is connected at the 30 foot location. Flushing is performed as with a normal well installation except there is no need to flush in the area of the plain pipe.

Notice particularly that since the internal diameter of the strainer and the well pipe in accordance with this invention are constant throughout, the cup of the flushing tool assembly is easily moved the entire length without materially expanding and contracting. Also, since there are no internal projections from the screen forming the well strainer, leakage within the channel from the isolated passage is held to a minimum.

While only a single embodiment of the invention has been described, it is obvious that numerous changes can be made without departing from the scope of the invention. For example, it has already been suggested that a male connector can be used instead of the female connector illustrated in FIG. 5. It was also noted that weld beads of various configuration can be used to bond the consecutive convolutions of the wire screen together.

Also, another method which might be used for setting the limit of radial expansion of the mandrel prior to the wrapping process is through the placement of longitudinal stops critically positioned for arresting the movement of the rod when the mandrel has expanded by the proper radial amount.

We claim:

1. In apparatus for manufacturing a well strainer from a metal wire by a helical winding operation, the combination of an expandable cylindrical mandrel comprising a first section at least equal in length to the well strainer and of transverse cross section describing an are slightly less than degrees, and a second section having an end portion of cylindrical form, and

an extending portion that mates with said first section so that together said first section and said extending portion form substantially a cylinder capable of expanding to an outside diameter equal to the inside diameter of the well strainer, said mandrel being adapted to be rotated relative to the metal wire whereby such wire can be wound thereon,

a plurality of two-part tapered flange assemblies, each assembly defining a two-part conical internal surface, the assemblies being axially spaced from one another and internally secured one part in each of said first and second sections of said mandrel, the tapered flange assemblies being positioned within the portion of the mandrel upon which wire is wound,

a reciprocable rod having a plurality of axially spaced externally tapered, conically surfaced members for separately mating with said flange assemblies to expand said first section radially with respect to said second section.

means for limiting the expansion of said first section of said mandrel when the external diameter of the mandrel equals the internal diameter of the well strainer,

means for securing the metal wire near the first end of said mandrel during the winding operation, and

means for securing the metal wire near the second end of said mandrel following the completion of the winding operation.

2. An apparatus for manufacturing a well strainer from a metal wire by a helical winding operation in accordance with claim 1, wherein said means for limiting the expansion of said first section includes a limiting collar of inside diameter equal to the inside diameter of the well strainer to limit the expansion of said first section.

3. In apparatus for manufacturing a well strainer from a metal wire by a helical winding operation, the combination of an expandable cylindrical mandrel comprising a first section at least equal in length to the well strainer and of transverse cross section describing an arc, and

a second section having an end portion of cylindrical form, and

an extending portion at least equal in length to the well strainer and of transverse cross section describing an are so that together said first section and said extending portion form essentially a cylinder capable of expanding to an outside diameter equal to the inside diameter of the well strainer,

said mandrel being adapted to be rotated relative to the metal wire whereby such wire can be wound thereon,

a plurality of multiple-part conical flanges each of which is internally secured one part in each of said sections of said mandrel, the flanges being axially spaced from one another along the cylindrical mandrel,

a reciprocable rod having external conical surfaces for separately mating with said flanges to expand said flanges to expand said sections radially with respect to the longitudinal central axis of said rod,

means for limiting the expansion of said sections of said mandrel when the external diameter of the mandrel equals the internal diameter of the well strainer,

means for securing the metal wire near the first end of said mandrel during the winding operation, and

means for securing the metal wire near the second end of said mandrel following the completion of the winding operation.

4. An apparatus for manufacturing a well strainer from a metal wire by a helical winding operation in accordance with claim 3, wherein said means for limiting the expansion of said section includes a limiting collar of inside diameter equal to the inside diameter of the well strainer to limit the expansion of said sections.

5. An apparatus for manufacturing a well strainer from a metal wire by a helical winding operation in accordance with claim 4, wherein said means for securing the metal wire near the first end of said mandrel includes a holding pin screwed through an internally threaded hole in said collar into a recess for receiving one end of the wire,

whereby said holding pin is tightened to hold the wire end between said holding pin and said mandrel.

References Cited UNITED STATES PATENTS 463,759 11/1891 Monjeau 166--232 716,555 12/1902 King 72144 771,902 10/1904 Frank 92.2 1,846,767 2/1932 Steuer et a1. 14092.2 2,811,882 11/1957 Hess 166232 3,275,785 9/1966 Wilson 140-71 CHARLES W. LANI-IAM, Primary Examiner L. A. LARSON, Assistant Examiner US. Cl. X.R. 

